When a defective disk has been removed from between two vertebrae it is necessary to provide an implant to maintain a spacing between these vertebrae so that the spine is not unstable in the region of the resected disk and to prevent the two bones from rubbing painfully together. As a rule such implants are generally closed cages whose interiors are only accessible through small apertures in their side walls. Bone chips must be introduced into the interior of such an implant so the two flanking vertebrae will grow and fuse together. This is a fairly difficult job, and necessitates the use of tiny bone fragments that do not grow well and that are quite hard to handle. Furthermore the job of packing the implant can take quite some time due to the smallness of the bone fragments, making the operation fairly long and, hence, even more expensive and dangerous for the patient than is strictly necessary.